DEBT - INTEREST EXPENSE COMPONENTS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017		Jun. 18, 2013
Debt Instrument [Line Items]
Non-cash amortization of discount on Convertible Notes			$ 91	$ 13,915	[1]
Amortization of debt issuance costs			32	482	[1]
Convertible Debt | 1.00% Convertible Notes due 2018
Debt Instrument [Line Items]
Interest rate						1.00%
Cash interest expense (coupon interest expense)	$ 0	$ 130	1	579
Non-cash amortization of discount on Convertible Notes	0	8,678	91	13,915
Amortization of debt issuance costs	0	263	3	423
Total interest expense related to Convertible Notes	$ 0	$ 9,071	$ 95	$ 14,917

[1] Prior period amounts have been adjusted retrospectively to reflect the adoption of ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. Refer to Note 1 for further discussion.